So, I think to fully enjoy these characters, you need to watch the spin offs especially the Chase one, if nothing else.

As for Drive and it's characters, here's what I think.

Drive had some fantastic characters and ideas especially the writing was strong and the antagonists were so well fleshed out when they become anti heroes or just victims of the main antagonists manipulative ways, everyone from Heart, to Brain, to Medic, I felt for them all. But while still a great show, I felt it lacking in some regions - first off Chase. Let's face it Chase was supposed to be the guy everyone was supposed to root for, through his interaction with Kamen Riders and the team sure, but the set up was for Gou right? So, their relationship shouldn't have felt so lacking.

What I mean is, we only see them interacting as Kamen Riders, and barely at all in actual life. I know that Gou was shown as being tsundere and supposed to be stoic but they could still have had actual meaningful conversations like they did those two or three times. Because of this their bromance felt incomplete. When the relationship between Heart and Brain, Heart and Shin Heart Chase was done so well. Even Shin and Gou was better than Gou and Chase. And the thing is its not like there was a lot going on plot wise in the beginning and Chase was introduced pretty early anyway.

The other minor gripe is the beginning part not being as interesting as the second part. Basically this was the time they could have used to develop Chase and Gou and both these problems could have been solved easily.
And okay I love Ryoma he's really done a good job but characters wise I just LOVE Heart Chase, and Gou!!!

But the thing about Drive and the reason I'm rating it high, despite those issues is because much like Build and W, Drive characters are the type that wont leave you alone. You keep wanting to go back. So this one and the spin offs have great re watch value for me.